Update actions/checkout action to v6 (#129)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

.github/workflows/CI.yml

@@ -7,7 +7,7 @@ jobs:
     runs-on: macOS-26
 
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
 
     - name: Read Xcode version
       id: xcode_version